If a hereditary predisposition to colorectal cancer or breast cancer is diagnosed, most guidelines state that clinical geneticists should request index patients to inform their at-risk relatives about the existence of this condition in their family, thus enabling them to consider presymptomatic genetic testing. Those identified as mutation carriers can undertake strategies to reduce their risk of developing the disease or to facilitate early diagnosis. This procedure of informing relatives through the index patient has been criticised, as it results in relatively few requests for genetic testing, conceivably because a certain number of relatives remain uninformed. This pilot study explored attitudes toward informing family members and relevant practices among clinical geneticists. In general, clinical geneticists consider it to be in the interests of family members to be informed and acknowledge that this goal is not accomplished by current procedures. The reasons given for maintaining present practices despite this include clinical ‘mores’, uncertainty about the legal right of doctors to inform family members themselves, and, importantly, a lack of resources. We discuss these reasons from an ethical point of view and conclude that they are partly uninformed and inconsistent. If informing relatives is considered to be in their best interests, clinical geneticists should consider informing relatives themselves. In the common situation in which index patients do not object to informing relatives, no legal obstacles prevent geneticists from doing so. An evaluation of these findings among professionals may lead to a more active approach in clinical practice